I don't see anything wrong with this. However I would not do it myself. I have no issues being productive throughout the day.
Can this drug be abused? If there are no harmful side effects all should be good to go!
Any drug can be abused. Although that doesn't mean it shouldn't be used, it does mean you have to be careful. There is also the question of short-term effectiveness versus long-term consequences. Strong stimulants are definitely effective in the short term, but they come with costs. Actually, in the short-term, smoking helps users focus, and quite effectively. The damage doesn't show up immediately. And short-term effects are much easier to see and research than long-term effects. So benefits might be easier to see than damages.